1. Field of the Invention
The present invention relates to an apparatus for supplying air or other fluid to a user on demand. More particularly, the present invention relates to such an apparatus for use in an underwater breathing system, such as a Scuba system.
2. Description of the Prior Art
Scuba diving is a sport enjoyed around the world. Diving as a sport has been around for several decades, but it has only been in the past decade that the dive industry has attempted to make dive gear that is comfortable, attractive, compact and light weight.
Conventional scuba regulators consist essentially of two parts. A first stage fits on the tank, which is attached to the user's back. The tank contains air or other gas pressurized to between 2,000 and 4,000 psi when full. The first stage lowers the air pressure of the air leaving the tank to a constant pressure of about 130 psi above the ambient pressure out of "lower pressure" port, regardless of the remaining tank pressure.
Conventionally, the air from the first stage flows to the second stage through a flexible tube. A typical prior art second stage regulator is shown in U.S. Pat. No. 3,991,785. In this patent, a diaphragm is movable in response to the inhalation of the user. Inhalation can cause the diaphragm to move a spring loaded lever arm of a valve which releases pressurized air coming from the first stage. Thus, air is supplied to the user on demand as the user begins inhalation. Upon the user exhaling, the diaphragm returns to its original position, thus permitting the valve to close, while the exhaled gas is removed from the regulator through an appropriate exhaust valve.
However, these conventional regulators had two serious shortcomings. First, they were quite bulky, particularly the large pressure sensitive inhalation diaphragm which operated the second stage valve. This large size was not only unattractive, but also resulted in the regulators being so heavy that divers tended to get sore jaws following a long dive.
However, such a large size for the regulator could not be avoided because of the need to provide sufficient force on the second stage valve to force the valve open without excessive inhalation effort. Reducing the diaphragm size would have made breathing very difficult.
An alternative approach is shown in U.S. Pat. No. 2,875,756. Here, the second stage regulator, including a large diaphragm are located within a casing positionable on the tank. An intake conduit provides an inhalation signal to the diaphragm for opening the second stage valve while a delivery conduit directs the air to the mouthpiece. Although this design has the advantage of reducing the bulk at the mouthpiece, the positioning of the regulator, particularly the inhalation diaphragm for opening and closing the second stage valve, at the tank introduces several problems. First, the long intake conduit results in increased resistance during the initial inhalation, which makes breathing more difficult. More significantly, the diaphragm is not located at the same level as the head of the user so that a difference can exist between the pressure sensed by the diaphragm and the pressure to which the user is subjected. For example, during horizontal swimming the tank is located above the user and the regulator thus senses a lower pressure than that experienced by the user, resulting in insufficient air pressure delivered to the mouthpiece.
Recently, an improved type of regulator has appeared which overcomes some of the problems of the conventional regulator. These regulators, known as "servo assisted" regulators use a pneumatic amplifier system in the second stage to amplify the diver's breathing signal. One such system is shown in U.S. Pat. No. 4,219,017. In this prior art device, the second stage of the regulator is completely contained within a casing attached to the mouthpiece. In this device, the pressure sensitive inhalation diaphragm movable in response to user demand does not control the air supply valve but instead controls a sensitive pilot valve through a control lever. The pilot valve can be easily opened with a small breathing effort, thus permitting a reduction in the size of the regulator diaphragm. According to this prior art patent, the air supply valve includes a restriction which permits air to enter a control chamber between the air supply valve and the pilot valve. The air supply valve is in the form of a second diaphragm which is sensitive to pressure changes in the control chamber. Thus, the opening of the pilot valve causes a pressure drop in the control chamber which opens the air supply valve and thereby provides air to the user. It can thus be seen that the user's efforts are amplified so that breathing is possible without great effort, and without the need for a large regulator diaphragm.
However, the design of U.S Pat. No. 4,219,017 has an important shortcoming. Although the diaphragm area can be greatly reduced, the additional structure required by the pilot valve and control chamber, as well as the complexity of the air supply valve require that the casing to which the mouthpiece is attached be almost as big as a conventional regulator. Indeed, the volume of the smallest servo assisted regulator is about 70% of the volume of the conventional large diaphragm regulator. Therefore, the problems of unsightly appearance and excessive weight associated with the prior art remain.